In the United States, all adult patients with a history of anaphylaxis in insect sting and a positive venom skin test are treated with whole body extracts. We have shown that, contrary to this standard treatment for insect sting allergy, venom immunotherapy is effective. Recently, investigators in Holland have found that if they sting history-positive skin test-positive patients, more than 70% have no reaction, and they contend, need no therapy. Incomplete US studies found fewer non-reactors on challenge sting. Neither the US nor the Dutch investigators have been able to develop diagnostic parameters to predict which patients will react to sting and which will not. The current proposal is based on the hypothesis that the European studies are, in part, correct and that it is unnecessary to treat as many patients as we do now. We will repeat their work focusing on patients with milder reactions, and address a flaw in that study, i.e., the question of whether a single sting predicts the reaction to subsequent stings. We also hypothesize that clinical protection from allergen immunotherapy results from a mechanism of immunization unrelated to IgG blocking antibodies. Immunotherapy with allergen peptides leads to a lesser immediate allergic response on re-exposure to allergen. We will immunize patients with peptides from antigen 5, the major yellow jacket venom allergen. Standard immunotherapy with venom proteins leads to frequent large local reactions and, less often, to systemic anaphylaxis. Peptide immunotherapy does not cause any immediate reactions, but there is often a delayed and mild "anaphylactic-like" response which we believe is due to the generation of an HRF-like cytokine. We have developed a detailed protocol to ascertain the nature of this response. Finally, the major goal of these studies is to use the stings of a hundred or more patients to develop parameters which predict which individuals will have a reaction to a sting. In the current work, we plan to study not only immunoglobulin levels, but also inflammatory cell activation, cytokine production, blood and urine histamine levels and tryptase levels. Further, based on the results of earlier studies, we will also study the state of activation of the kinin coagulation pathways. Venom immunotherapy (VIT) is recommended based on perceived high risk (>50%) of future systemic reaction (SR), fear of worsening SR and lack of specific prognostic test. This sting challenge program seeks to define clinical and laboratory characteristics associated with lower risk of SR in patients with SR history and positive venom skin tests (VST). Insect stings were performed in a monitored clinical setting and patients were observed for objective signs and subjective symptoms of SR. Since the last progress report, 603 respondants to our advertisements have been screened by telephone, but only 102 were willing and eligible for in- clinic evaluations in this study year, of whom 37 new patients completed a deliberate sting challenge during the summer of 1998. Of these patients, 23 (62%) had no reaction to the challenge and another 7 (19%) had questionable clinical responses (subjective symptoms only). Objective evidence of systemic reaction occurred in 7 (19%) patients, with 5 mild, 2 moderate and no severe reactions. This relatively low reaction rate is similar to the results in our first 58 patients in 1997, and probably related to the somewhat less severe histories in these volunteers, and the fact that we did not sting the most severe patients. The results confirm that mild to moderate reactors are at a lower risk than severe reactors (p<0.03). Thus far, no case has occurred in which the challenge reaction was worse than the previous systemic sting reaction. Patients from last year and this year have had repeat stings performed, with a total of 95 patients participating (receiving 160 stings), and an overall reaction rate of 20%. The results to date support our hypothesis that the majority of patients currently eligible for venom immunotherapy (VIT) may not need treatment. Our results also give us early confirmation that we have powered this study appropriately to ensure significant results, since some results are already statistically significant and others are approaching significance. The existing plan for additional sting challenges of many patient types over the next 18 months will provide the power to analyze the role of many different clinical and laboratory parameters.